During a serious fire virtually everything is damaged that has not been specially protected, and much is totally destroyed. In a fire of this nature, it is almost universally found that the one spot within the dwelling in a house fire that survived largely untouched by the heat is the refrigerator compartment. The insulated walls of the refrigerator last long enough so that except in the worst of fires, the fire is out before the temperature within the refrigerator approaches the flash point of paper. In fact, it is common to find frozen foods that are still frozen after the rest of the house has been incinerated.
The refrigerator, therefore, would be a good place to store compact valuables which are susceptible to heat damage or destruction such as wills, bond certificates, stock certificates, rare currency bills, etc. Rather than putting the items loosely in a refrigerator or in a shoe box, with the incumbent problem that it would soon become apparent to all that valuables are kept in a box in the refrigerator, it would be desirable to disguise the cache somehow and at the same time provide an additional layer of protection against fire even beyond the walls of the refrigerator.